The liquid crystal display device has widely been used due to advantages of light weight, low power consumption, low working voltage and non-radiation and the like. The liquid crystal display device includes a display panel and a backlight module, and the display panel includes opposed substrates and a liquid crystal layer between the opposed substrates. Liquid crystal molecules in the display panel do not emit light themselves, so they need a backlight module to provide backlight for them. Therefore, the quality of the backlight module concerns the display quality of the liquid crystal display device, and it is one of the important components of a liquid crystal display device.